In recent years, a battery having a negative electrode composed of a carbonaceous material such as graphite and a positive electrode composed of a lithium-containing metal oxide such as LiCoO2 has been developed. This battery is the so-called rocking chair-type battery that lithium ions are supplied to the negative electrode from the lithium-containing metal oxide making up the positive electrode by charging after assembly of the battery, and the lithium ions are then returned to the positive electrode from the negative electrode by discharging, is called a lithium ion secondary battery because only lithium ions participate in charge/discharge without using metal lithium in the negative electrode and is distinguished from a lithium battery using lithium metal. This lithium ion secondary battery is characterized by high voltage, high capacity and high safety.
Under the circumstances that environmental problems are greatly taken up, developments of a storage system of clean energy by solar photovoltaic power generation or wind power generation and a power source used in electric cars or hybrid electric cars taking the place of gasoline cars have been energetically made. More recently, with the development of high-performance and high-function devices and equipments for automotive use, such as power windows and IT-related instruments, there has been a demand for development of a new power source having a high energy density and a high power density.
As an accumulator meeting uses of which high energy density and high power density properties are required, attention has been recently paid to an accumulator called a hybrid capacitor with the principles of electricity accumulation in the lithium ion secondary battery and the electric double layer capacitor combined. As such a hybrid capacitor, there has been proposed an organic electrolyte capacitor having a negative electrode composed of a carbonaceous material capable of occluding and deoccluding lithium ions, by which a high energy density is achieved by lowering the potential of the negative electrode by causing lithium ions to be occluded and supported (hereinafter also referred to as “doped”) in the carbonaceous material in advance by a chemical method or electrochemical method (see, for example, Patent Literature 1).
In such an organic electrolyte capacitor, high performance is expected. However, the capacitor involves problems that it takes an extremely long time to dope the negative electrode with lithium ions in advance and that it is necessary to uniformly support the lithium ions in the whole negative electrode, and thus it was said that difficulty is encountered on putting the capacitor to practical use as, in particular, a large-scale and high-capacity cell such as a cylindrical battery with electrodes wound or a rectangular battery with a plurality of electrodes laminated.
In order to solve these problems, there has been proposed a wound-type accumulator comprising a cylindrical wound electrode unit equipped with a positive electrode and a negative electrode that each have a current collector with pores passing through from a front surface to a back surface formed therein, said negative electrode being composed of a negative electrode active material capable of reversibly supporting lithium ions, said positive electrode and negative electrode being wound in a state stacked on each other through a separator, and a lithium ion source provided on any of an outer peripheral surface and an inner peripheral surface in the wound electrode unit, wherein the negative electrode is doped with lithium ions by electrochemical contact of the negative electrode with lithium metal (see, for example, Patent Literature 2).
In this wound-type accumulator, the pores passing through from the front surface to the back surface are provided in the current collectors, so that the lithium ions are not interrupted by the current collectors even when the lithium ion source is arranged on any of the outer peripheral surface and the inner peripheral surface in the wound electrode unit, and move between the electrodes through the pores in the current collectors, whereby not only a negative electrode portion near to the lithium ion source, but also a negative electrode portion distant from the lithium ion source can be electrochemically doped with the lithium ions.
In the negative electrode obtained by doping a carbonaceous material or the like, which can occlude and deocclude lithium ions, with the lithium ions in advance, the potential thereof becomes lower than active carbon used in the electric double layer capacitor as described above, so that withstand voltage in a cell combined with a positive electrode active carbon is improved, and since the capacity of the negative electrode is extremely large compared with the active carbon, a high energy density is achieved by the wound-type accumulator equipped with this negative electrode.
However, in such a wound-type accumulator, the lithium metal is provided on only any one of the outer peripheral surface and the inner peripheral surface of the electrode element, so that this accumulator involves a problem that it takes a long time to uniformly dope the whole negative electrode with lithium ions. When the lithium ion source is provided on only the outer peripheral surface of the wound electrode unit, high voltage and high capacity are achieved, but the amount of the lithium ions to dope becomes large, so that it is necessary to use a lithium ion source having a great thickness and thus there is a problem that a packing amount of the electrodes becomes low to encounter difficulty on achieving a sufficiently high energy density.
In order to solve such a problem, there has been proposed a wound-type accumulator comprising a cylindrical wound electrode unit configured by winding a positive electrode with an electrode layer containing a positive electrode active material capable of reversibly supporting lithium ions and/or anions formed on at least one surface of a current collector having pores passing through from a front surface to a back surface, and a negative electrode with an electrode layer containing a negative electrode active material capable of reversibly supporting lithium ions formed on at least one surface of a current collector having pores passing through from a front surface to a back surface in a state stacked on each other through a separator, and lithium ion sources provided on both outer peripheral surface and inner peripheral surface in the wound electrode unit, wherein the negative electrode and/or the positive electrode is doped with lithium ions by electrochemical contact of the negative electrode and/or the positive electrode with the lithium ion sources (see, for example, Patent Literature 3).